The iron nitrogenase reduces carbon dioxide to formate and methane under physiological conditions: A route to feedstock chemicals.

Nitrogenases are the only known enzymes that reduce molecular nitrogen (N) to ammonia. Recent findings have demonstrated that nitrogenases also reduce the greenhouse gas carbon dioxide (CO), suggesting CO to be a competitor of N. However, the impact of omnipresent CO on N fixation has not been investigated to date. Here, we study the competing reduction of CO and N by the two nitrogenases of , the molybdenum and the iron nitrogenase. The iron nitrogenase is almost threefold more efficient in CO reduction and profoundly less selective for N than the molybdenum isoform under mixtures of N and CO. Correspondingly, the growth rate of diazotrophically grown strains relying on the iron nitrogenase notably decreased after adding CO. The in vivo CO activity of the iron nitrogenase facilitates the light-driven extracellular accumulation of formate and methane, one-carbon substrates for other microbes, and feedstock chemicals for a circular economy.